Method and system for impairment shifting

ABSTRACT

A method and system for impairment shifting is disclosed and may include receiving one or more radio frequency (RF) analog television signals in a receiver of a communication device, downconverting the received one or more received RF analog television signals to baseband frequencies, synchronizing the receiver to the one or more received RF analog television signals, and adjusting a frequency of one or more local oscillators in the receiver to configure in-phase/quadrature (I/Q) mismatch of a picture carrier signal to fall near a sound carrier signal in the received RF analog television signals. The frequency of the one or more local oscillators may be adjusted to configure a DC offset impairment to fall between luminance and chrominance harmonics at baseband in the analog television signals. I/Q imbalanced impairments may be configured with about 300 kHz separation from the sound carrier signal.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a continuation of application Ser. No. 13/371,932filed on Feb. 13, 2012, which makes reference to and claims priority toU.S. Provisional Application Ser. No. 61/544,922 filed on Oct. 7, 2011.Each of the above stated applications is hereby incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

Certain embodiments of the invention relate to wireless communication.More specifically, certain embodiments of the invention relate to amethod and system for impairment shifting.

BACKGROUND OF THE INVENTION

Television providers have moved significantly toward cable and satellitetechnology for providing content to users, but terrestrial transmissionstill has significant usage worldwide. Analog television signals arestill utilized in many areas of the world, and are also utilized inportions of digital provider networks.

Receivers introduce undesirable impairments to a signal when the signalis being amplified, filtered or downconverted. For example, directconversion receivers (also referred to as “DCR”, “zero IF receivers”, or“ZIF receivers”) are a very efficient way of implementing a radioreceiver. However these receivers introduce a variety of impairments toa signal which can degrade overall performance of the system. Mostnotably, DC offset and signal image due to imbalances in the complexsignal path, often referred to as “I/Q mismatch,” may corrupt thedownconverted signal. Existing methods for performing DC offsetcancellation (DCOC) and I/Q calibration (IQ cal) can be effective atmitigating these problems. However, for signals which require very highsignal to noise ratio such as analog TV signals, the residual impairmentdue to the limitations of these techniques can still leave visibleartifacts in the analog picture screen.

Further limitations and disadvantages of conventional and traditionalapproaches will become apparent to one of skill in the art, throughcomparison of such systems with the present invention as set forth inthe remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for impairment shifting, substantially as shownin and/or described in connection with at least one of the figures, asset forth more completely in the claims.

Various advantages, aspects and novel features of the present invention,as well as details of an illustrated embodiment thereof, will be morefully understood from the following description and drawings.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of an exemplary communication device with impairmentshifting, in accordance with an embodiment of the invention.

FIG. 2 is a diagram illustrating an exemplary receiver with impairmentshifting, in accordance with an embodiment of the invention.

FIG. 3 is a diagram illustrating an exemplary analog televisionspectrum, in accordance with an embodiment of the invention.

FIG. 4 is a diagram illustrating exemplary television spectra with a DCoffset signal, in accordance with an embodiment of the invention.

FIG. 5 is a diagram illustrating an exemplary television spectrum withimage signals, in accordance with an embodiment of the invention.

FIG. 6 is a block diagram illustrating exemplary steps for impairmentshifting in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the invention may be found in a method and system forimpairment shifting. Exemplary aspects of the invention may comprisereceiving one or more radio frequency (RF) signals in a receiver in acommunication device, downconverting the received one or more receivedRF signals to baseband frequencies, and synchronizing the receiver tothe one or more received RF signals. The frequency of one or more localoscillators in the receiver may be adjusted to shift a DC impairmentsignal to fall between desired baseband signals from the received RFsignals. The one or more received RF signals may comprise analogtelevision signals. The frequency of the one or more local oscillatorsmay be adjusted to configure the DC offset impairments to fall betweenluminance and chrominance harmonics at baseband in the analog televisionsignals. The frequency of the one or more local oscillators may beadjusted to configure an in-phase/quadrature (I/Q) imbalanced impairmentcaused by residual in-phase and quadrature mismatch of a picture carriersignal to fall near a sound carrier signal in the analog televisionsignals. The frequency of the one or more local oscillators may beadjusted to configure an I/Q imbalanced impairment caused by residualin-phase and quadrature mismatch of a sound carrier signal to fallbetween luminance and chrominance harmonics at baseband in the analogtelevision signals. In-phase and quadrature signals may be processed inthe receiver. The one or more received RF signals may comprise satellitetelevision signals or cable television signals. The receiver maycomprise a direct conversion receiver.

FIG. 1 is a diagram of an exemplary communication device with impairmentshifting, in accordance with an embodiment of the invention. Referringto FIG. 1, there is shown the receiving device 101 comprising a radiofrequency (RF) module 105, an RF-to-baseband conversion module 107, afrequency control module 109, a baseband module 111, a processor 113,and a memory 115.

The RF module 105 may comprise one or more RF receive (Rx) and transmit(Tx) paths for receiving signals from a satellite system, cable TVhead-end, and/or terrestrial TV antennas, for example. The RF module 105may comprise impedance matching elements, LNAs, power amplifiers,variable gain amplifiers, and filters, for example. The RF module 105may thus be operable to receive, amplify, and filter RF signals beforecommunicating them to the RF-to-baseband module 107.

The RF-to-baseband module 107 may comprise mixers and local oscillatorsthat may be operable to receive RF signals and down-convert them tobaseband signals for further processing by the baseband module 111. TheRF-to-baseband module 107 may comprise in-phase and quadrature mixersfor use with polar signals, for example.

The local oscillators may be tunable such that a plurality of RFfrequencies may be received and down-converted to baseband. In anexemplary embodiment, the local oscillators may be tuned to positionimpairments between desired signals to reduce the impairments effect ondesired signals. The frequency of the local oscillators may beconfigured by the frequency control module 109.

The frequency control module 109 may comprise circuitry operable tocontrol the frequency of the local oscillators, and may comprise crystaloscillators, frequency dividers, and an impairment shift calculationmodule for configuring the frequency of the local oscillators such thatimpairments fall between desired signals at baseband as opposed tointerfering with the desired baseband signals.

The baseband module 111 may comprise circuitry operable to processreceived baseband signals. For example, the baseband module 111 maycomprise filters and amplifiers for further processing of the selectedbaseband signals. In addition, the baseband module 111 may comprise oneor more analog-to-digital converters (ADCs) to convert the receivedanalog signals to digital signals for processing by the processor 113.

The processor 113 may comprise a general purpose processor, such as areduced instruction set computing (RISC) processor, for example, thatmay be operable to control the functions of the wireless device 101. Forexample, the processor 113 may configure the frequency control module109 to shift impairments between desired signals so as to reduce oreliminate interference. Additionally, the processor 113 may demodulatebaseband signals received from the baseband module 111.

The memory 115 may comprise a programmable memory module that may beoperable to store software and data, for example, for the operation ofthe wireless device 101. Furthermore, the memory 115 may store thefrequency configurations performed by the frequency control module 109.

Receivers introduce undesirable impairments to a signal when the signalis being amplified, filtered or downconverted. For example, directconversion receivers, which may also be referred to as “DCR”, “zero IFreceivers”, or “ZIF receivers”, are a very efficient way of implementinga radio receiver. However, they introduce a variety of impairments to asignal which can degrade overall performance of the system.

Most notably, DC offset and signal images due to imbalances in thecomplex signal path (often referred to as I/Q mismatch) may corrupt thedowncoverted signal. Methods for performing DC offset cancellation andI/Q calibration may be effective at mitigating these problems. However,for signals which require very high signal to noise ratio, such asanalog TV signals, the residual impairment due to the limitations ofthese techniques can still leave visible artifacts in the analog picturescreen.

In a direct conversion receiver, the DC offset is introduced at thefrequency to which the local oscillator is tuned. This can be due toself-mixing, circuit offset voltages/currents, or nonlinearities, forexample. The I/Q mismatch impairment may be introduced by the signalfolding on itself about the local oscillator frequency. For the signalswhich require very high signal to noise ratio, such as analog TVsignals, the residual impairments due to the limitations of DC offsetcancellation or IQ imbalance calibrations may still interfere withpicture or chroma carriers or their harmonics, and leave visibleartifacts in the screen.

Furthermore, the limited frequency accuracy over individual crystals orcrystal temperatures makes the actual local oscillator frequencyunpredictable, which leads to unavoidable interferers of residualimpairments and carrier harmonics. The device 101 may thus be operableto configure the local oscillator precisely via the frequency controlmodule 109, and thereby control where these impairments fall within thereceived signal.

FIG. 2 is a diagram illustrating an exemplary receiver with impairmentshifting, in accordance with an embodiment of the invention. Referringto FIG. 2, there is shown a receiver 200 comprising a low noiseamplifier (LNA) 201, I and Q mixers 203A and 203B, local oscillators(LOs) 205A and 205B, frequency control modules 207A and 207B, crystaloscillators 209A and 209B, analog-to-digital converters (ADCs) 211A and211B, gain blocks 213A and 213B, a processing module 215, a carrierdetect module 217, and a local oscillator adjust calculation module 219.There are also shown an input RF signal RF In 221 and local oscillatorsignals LO_I and LO_Q.

The LNA 201 may be operable to provide amplification to the signal RF In221 with the amplified signal being communicated to the mixers 203A and203B. The signal RF In 221 may be down-converted to in-phase andquadrature signals in the I path and Q path in the receiver 200.

The mixers 203A and 203B may comprise circuitry that is operable togenerate output signals at frequencies that are the sum and thedifference between the input RF signal RF In 221 and the localoscillator signal, which comprises either LO_(I) or LO_(Q). Thefrequency of LO_(I) and LO_(Q) may be configured such that the desiredsignal is near zero frequency and other signals may be filtered out by alow pass filter, for example. The phase of the signals LO_(I) and LO_(Q)may be 90 degrees out of phase, thereby enabling the processing ofin-phase and quadrature signals.

The local oscillators 205A and 205B may comprise circuitry that isoperable to generate an RF signal to enable down-conversion of RFsignals received by the mixers 203A and 203B, respectively. The localoscillators 205A and 205B may comprise voltage-controlled oscillators,for example, whose frequency of oscillation may be configured by acontrol voltage.

The frequency control modules 207A and 207B may comprise circuitryoperable to generate a control signal for the local oscillators 205A and205B. The frequency control modules 207A and 207B may comprisephase-locked-loops, frequency dividers and multipliers, filters, andother components for configuring the frequency of a local oscillator.The frequency control modules 207A and 207B may receive as an input, anadjustment signal from the LO adjust calculation module 219. Thefrequency control modules 207A and 207B may also comprise phase offsetcapability for configuring LO signals 90 degrees out of phase fordown-converting I and Q signals.

The crystal oscillators 209A and 209B may comprise stable clock sourcesfor the receiver 200, and may comprise a piezoelectric crystal, forexample, that outputs a stable clock signal at a given temperature. Inanother exemplary embodiment, the clock signals communicated to thefrequency control modules 207A and 207B may be generated by a singlecrystal oscillator.

The ADCs 211A and 211B may comprise circuitry that is operable toconvert analog input signals to digital output signals. Accordingly, theADCs 211A and 211B may receive baseband analog signals from the mixers203A and 203B and may generate digital signals to be communicated to thegain blocks 213A and 213B.

The gain blocks 213A and 213B may comprise digital gain modules forproviding a programmable gain level to received digital signals prior tosubsequent processing by the processing module 215.

The processing module 215 may comprise a processor similar to theprocessor 113, for example, described with respect to FIG. 1.Accordingly, the processing module 213 may be operable to control thefunctions of the receiver 200 and may process received baseband signalsto demodulate, deinterlace, and/or perform other video processingtechniques to the data.

The carrier detect module 217 may comprise circuitry for determining thelocation of impairments with respect to desired signals. Accordingly,the carrier detect module 217 may be operable to assess the relativeamplitude of signals and their frequency to determine the location ofthe impairments. For example, the carrier detect module 217 may comparethe amplitude of a signal at a frequency where a chroma, picture, orsound signal is expected based on the LO frequency utilized todown-convert the received signals to baseband. In an exemplary scenario,the carrier detect module 217 may comprise a separate module and in analternate scenario, the carrier detect module 217 may comprise a part ofthe processing module 215.

The LO adjust calculation module 219 may comprise circuitry that isoperable to determine an adjustment factor for tuning the localoscillators 205A and 205B, such that impairments are positioned betweendesired signals at baseband, as opposed to causing interference. The LOadjust calculation module 219 may receive, as an input, a signal fromthe carrier detect module 217 comprising an assessment of the frequencyspectrum of the baseband signal generated by the down-conversion.Accordingly, the LO adjust calculation module 219 may determine that animpairment is interfering with a desired signal, and an outputadjustment signal may be communicated to the frequency control modules207A and 207B to result in the impairment falling between desiredsignals, where they are least visible.

FIG. 3 is a diagram illustrating an exemplary analog televisionspectrum, in accordance with an embodiment of the invention. Referringto FIG. 3, there is shown a television spectrum 300 comprising a picturesignal 301, a chroma signal 303, and a sound signal 305. The signals maybe down-converted to baseband by selecting a local oscillator signal ator near the desired frequency such that the resulting difference signalfalls near zero frequency. DC offset due to self-mixing, circuit offsetvoltages or currents, and or nonlinearities may interfere with thedown-converted desired signal. Existing methods for performing DC offsetcancellation (DCOC) can effectively mitigate the DC problems. However,for signals which requires very high signal to noise ratio such asanalog TV signal, the residual impairments due to the limitations ofthese techniques can still leave visible artifacts in the analog picturescreen. The residual impairments may be further mitigated by tuning thelocal oscillator frequency so that the DC offset signal falls betweendesired signal spectra, as described further in FIG. 4.

FIG. 4 is a diagram illustrating an exemplary television spectrum with aDC offset signal, in accordance with an embodiment of the invention.Referring to FIG. 4, there is shown an analog television spectra 400comprising picture signal 401 and associated harmonics P1-PN 401A-401N,a chroma signal 403 and associated harmonics C1-CN 403A-403N, a soundsignal 405, and a DC offset signal 407. Analog TV signals comprisepicture and chroma carriers which are modulated to produce harmonicmultiples of the modulation rate. For NTSC the harmonic spacing is15.734 kHz; for PAL it is 15.625 kHz.

In an exemplary scenario, the DC offset impairment may be mitigated by:(1) down-converting the signal with a direct conversion receiver, suchas the receiver 200, so that the desired signal overlaps with DC; (2)synchronizing to the received signal so that the receiver 200 maydetermine precisely where the impairment will occur within the receivedsignal; (3) adjusting the local oscillator of the receiver to shift theDC offset so that it falls in between desired features in the signal.

The synchronizing to a received signal may utilize phase lock loops,carrier recovery loops, or data recovery loops, for example. For analogTV signals, the DC offset may be positioned to fall somewhere betweenthe picture and chroma harmonics, as shown by the DC offset signal 407.In an exemplary scenario, the DC offset signal 407 may be located halfway between the picture harmonic PN 401N and the chroma harmonic CN403N, as illustrated in FIG. 4.

FIG. 5 is a diagram illustrating an exemplary television spectrum withimage impairments due to I/Q path imbalance, in accordance with anembodiment of the invention. Referring to FIG. 5, there is shown ananalog television spectra 500 comprising picture carrier signal 501 andassociated harmonics P1-PN 501A-501N, a chroma carrier signal 503 andassociated harmonics C1-CN 503A-503N, a sound signal 505, a DC offsetsignal 507, a sound image signal 509, and a picture image signal 511.

The I/Q path imbalance may due to inaccurate 90 degree phase differencebetween LO_(I) 205A and LO_(Q) 205B, or asymmetric path gain (or loss)in the analog baseband I/Q paths between the mixer 225 and the ADC 211in FIG. 2. Existing methods for performing I/Q calibration (IQ cal) caneffectively mitigate the image problems. However, for signals whichrequire very high signal to noise ratio such as analog TV signals, theresidual impairments due to the limitations of these techniques canstill leave visible artifacts in the analog picture screen.

The frequency spacing between the image impairment 511 and the DC offsetsignal 507 is indicated by +f_(image) and the spacing between thepicture carrier signal 501 and the DC offset signal 507 is indicated by−f_(image). Similarly, the frequency spacing between the sound signal505 and the DC offset signal 507 is indicated by +f_(image) _(_) _(sd)and the spacing between the sound image impairment 509 and the DC offsetsignal 507 is indicated by −f_(image) _(_) _(sd).

Since there are many carrier harmonics for the picture carrier signal501 and the chroma carrier signal 503, the receiver local oscillator maybe flexibly configured in order to choose between which harmonics the DCoffset falls. By changing the harmonic with respect to the DC offset,the image frequency f_(image) changes.

The image impairments may be mitigated by: (1) adjusting the LOfrequency such that the image of the picture carrier falls close to thesound carrier, this invention shifts the image outside of the desiredvideo bandwidth including Picture and Chroma signals and theirharmonics; and (2) adjusting the LO frequency such that the separationof the sound carrier signal 505 from the picture image 511, f_(os), islarger than the sound carrier's modulated bandwidth, which avoidsinterference with the sound signal. In an exemplary embodiment, thepicture image is positioned about 300 KHz away from the sound carrier.This reduces the impact that I/Q mismatch has on the quality of thevideo signal, since the picture carrier signal 501 is generally thestrongest component in the video signal. Similarly, the sound imagesignal 509 may be configured to fall between the picture harmonics P1-PN501A-501N, as shown between P3 501C and P4 501D in FIG. 5, which mayminimize the impact that I/Q mismatch has from sound carriers, to thequality of the video signal.

Relative to picture center carrier 501, as the LO frequency in thereceiver is adjusted, the DC offset signal 507 location may shift thesame amount as the LO frequency, while the picture image signal 511 andthe sound carrier image signal 509 move twice as much, which enables theabove positioning criteria to be met.

FIG. 6 is a block diagram illustrating exemplary steps for impairmentshifting in accordance with an embodiment of the invention. Theexemplary method illustrated in FIG. 6 may, for example, share any orall functional aspects discussed previously with regard to FIGS. 1-5.

Referring to FIG. 6, after start step 601, in step 603, RF input signalsmay be received by the RF front end receiver 105 of the device 101. TheRF input signals may be communicated from a cable television orsatellite television service provider or from terrestrial televisionsignals.

In step 605, the signals may be down-converted to baseband using one ormore mixers. In an exemplary scenario, two mixers with 90 degree offsetclock signals (LO_I and LO_Q) may generate in-phase and quadraturebaseband signals in each Rx path. The wireless device may comprise aplurality of Rx paths.

In step 607, the receiver may be synchronized to the received signal sothat it may determine precisely where the impairment will occur withinthe received signal. The synchronizing may be accomplished viaphase-locked loops, carrier recovery loops, or data recovery loops, forexample.

In step 609, the receiver local oscillator may be adjusted to shift theDC offset position so that it falls between desired features in thesignal. For example, in analog television signals, the DC offset may beconfigured between the picture and chroma harmonics, and in an exemplaryscenario may be configured to fall halfway between the picture andchroma harmonics to reduce or eliminate interference with desiredsignals. This is followed by end step 611.

In an embodiment of the invention, a method and system may comprisereceiving one or more radio frequency (RF) signals 221, 300 in areceiver 200 in a communication device 101, downconverting the receivedone or more received RF signals 221, 300 to baseband frequencies, andsynchronizing the receiver 200 to the one or more received RF signals221, 300.

The frequency of one or more local oscillators 205A and 205B in thereceiver 200 may be adjusted to shift a DC impairment 407, 507 to fallbetween desired baseband signals 401, 403, 405, 501, 503, 505 from thereceived RF signals 221, 300, 400, 500. The one or more received RFsignals 221, 300 may comprise analog television signals 300.

The frequency of the one or more local oscillators 205A and 205B may beadjusted to configure a DC impairment 407,507 to fall between luminanceand chrominance harmonics 401A-401N, 403A-403N, 501A-501N, and 503A-503Nat baseband in the analog television signals 300. The frequency of theone or more local oscillators 205A and 205B may be adjusted to configurean I/Q imbalanced impairment 511 caused by residual in-phase andquadrature mismatch of a picture carrier signal 401, 501 to fall near asound carrier signal 405, 505 in the analog television signals 300.

The frequency of the one or more local oscillators 205A and 205B may beadjusted to configure an I/Q imbalanced impairment 509 caused byresidual in-phase and quadrature mismatch of a sound carrier signal 405,505 to fall between luminance and chrominance harmonics 401A-401N,403A-403N, 501A-501N, and 503A-503N at baseband in the analog televisionsignals 300. In-phase and quadrature signals 223A, 223B, 225A, and 225Bmay be processed in the receiver 200. The one or more received RFsignals 221, 300 may comprise satellite television signals or cabletelevision signals. The receiver 200 may comprise a direct conversionreceiver.

Other embodiments of the invention may provide a non-transitory computerreadable medium and/or storage medium, and/or a non-transitory machinereadable medium and/or storage medium, having stored thereon, a machinecode and/or a computer program having at least one code sectionexecutable by a machine and/or a computer, thereby causing the machineand/or computer to perform the steps as described herein for impairmentshifting.

Accordingly, aspects of the invention may be realized in hardware,software, firmware or a combination thereof. The invention may berealized in a centralized fashion in at least one computer system or ina distributed fashion where different elements are spread across severalinterconnected computer systems. Any kind of computer system or otherapparatus adapted for carrying out the methods described herein issuited. A typical combination of hardware, software and firmware may bea general-purpose computer system with a computer program that, whenbeing loaded and executed, controls the computer system such that itcarries out the methods described herein.

One embodiment of the present invention may be implemented as a boardlevel product, as a single chip, application specific integrated circuit(ASIC), or with varying levels integrated on a single chip with otherportions of the system as separate components. The degree of integrationof the system will primarily be determined by speed and costconsiderations. Because of the sophisticated nature of modernprocessors, it is possible to utilize a commercially availableprocessor, which may be implemented external to an ASIC implementationof the present system. Alternatively, if the processor is available asan ASIC core or logic block, then the commercially available processormay be implemented as part of an ASIC device with various functionsimplemented as firmware.

The present invention may also be embedded in a computer programproduct, which comprises all the features enabling the implementation ofthe methods described herein, and which when loaded in a computer systemis able to carry out these methods. Computer program in the presentcontext may mean, for example, any expression, in any language, code ornotation, of a set of instructions intended to cause a system having aninformation processing capability to perform a particular functioneither directly or after either or both of the following: a) conversionto another language, code or notation; b) reproduction in a differentmaterial form. However, other meanings of computer program within theunderstanding of those skilled in the art are also contemplated by thepresent invention.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the present invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the present invention without departing from its scope.Therefore, it is intended that the present invention not be limited tothe particular embodiments disclosed, but that the present inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A method for communication, the methodcomprising: in a communication device comprising first and seconddownconverters and a processor: receiving, by the first down-converter,a radio frequency (RF) signal comprising a first desired signal and asecond desired signal; downconverting, by the first down-converter, theRF signal to a first baseband signal using a first oscillating signal;receiving the RF signal using the second down-converter; downconverting,by the second down-converter, the RF signal to a second baseband signalusing a second oscillating signal; receiving the first and secondbaseband signals in the baseband processor; and independentlycontrolling, using the processor, the first oscillating signal and thesecond oscillating signal to generate a DC offset impairment signallocated between the first desired signal and the second desired signalat baseband.
 2. The method according to claim 1, comprising processingin-phase and quadrature (I/Q) signals in said communication device. 3.The method according to claim 2, comprising controlling the first andsecond oscillating signals to configure I/Q imbalanced impairmentscaused by residual in-phase and quadrature mismatch of desired signalsto fall between the desired signals at baseband.
 4. The method accordingto claim 1, wherein the RF signal comprises a satellite televisionsignal.
 5. The method according to claim 1, wherein the RF signalcomprises a cable television signal.
 6. The method according to claim 1,wherein the communication device is a direct conversion receiver.
 7. Themethod according to claim 1, comprising detecting, using a carrierdetect module, a frequency of the impairment signal from assessment ofthe frequency spectrum of baseband signals generated by thedown-conversion by the first and second down-converters.
 8. The methodaccording to claim 7, comprising calculating frequency adjustments forthe first and second oscillating signals based on the detected frequencyof the impairment signal.
 9. The method according to claim 8, comprisingcontrolling the first and second oscillating signals based on thecalculated frequency adjustments.
 10. The method according to claim 1,comprising adjusting oscillators that generate the first and secondoscillating signals, the adjusting based on a control signal from aphase-locked loop.
 11. A system for communication, the systemcomprising: a first downconverter operable to receive a radio frequency(RF) signal comprising a first desired signal and a second desiredsignal, wherein the first downconverter is operable to convert the RFsignal to a first baseband signal using a first oscillating signal; asecond downconverter operable to receive the RF signal, wherein thesecond downconverter is operable to convert the RF signal to a secondbaseband signal using a second oscillating signal; and a processoroperable to receive the first baseband signal and the second basebandsignal, wherein the processor is operable to independently control thefirst oscillating signal and the second oscillating signal to generate aDC offset impairment signal located between the first desired signal andthe second desired signal at baseband.
 12. The system according to claim11, wherein the first and second downconverter are operable to processin-phase and quadrature (I/Q) signals.
 13. The system according to claim12, wherein the processor I operable to control the first and secondoscillating signals to configure I/Q imbalanced impairments caused byresidual in-phase and quadrature mismatch of desired signals to fallbetween the desired signals at baseband.
 14. The system according toclaim 11, wherein the RF signal comprises a satellite television signal.15. The system according to claim 11, wherein the RF signal comprises acable television signal.
 16. The system according to claim 11, whereinthe first and second down-converters and processor are in a directconversion receiver.
 17. The system according to claim 11, comprising acarrier detect module that is operable to detect a frequency of theimpairment signal from assessment of the frequency spectrum of basebandsignals generated by the down-conversion by the first and seconddown-converters.
 18. The system according to claim 17, comprising alocal oscillator control module that is operable to calculate frequencyadjustments for the first and second oscillating signals based on thedetected frequency of the impairment signal.
 19. The system according toclaim 18, comprising a frequency control module that is operable tocontrol the first and second oscillating signals based on the calculatedfrequency adjustments.
 20. The system according to claim 19, wherein thefrequency control module is operable to adjust oscillators that generatethe first and second oscillating signals, the adjusting based on acontrol signal from a phase-locked loop.